Creating New Data: Using Puck or Scanner (Especially for GATE-Geospatial 2022)

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For spatial data, the use of a Digitizer is standard. The digitizer is more advanced and much more accurate version of input device. Many different types of input data are used for input data into a computer.

This Diagram Shows Types of Input Data

Factors Affecting the Selection of Digitizer

There are two main kinds of digitizers- puck and scanners. Factors that affect the selection of digitizer include:

This Diagram Shows Factors Affect the Selection of Digitizer
  • Stability deals with the exact reading of the digitizer.
  • Repeatability is synonym for precision here means if you place the puck in the same exact location twice, how close will the first and second readout be?
  • Linearity is a measure of the ability of the digitizer to be within a specified distance of the correct value as the puck is moved over large distance.
  • Skew is a measure of the squareness of the results on a tablet: do coordinates located at the four corners of digitizer produce a true rectangle?

Puck

To enhance the accuracy of such device, the degree of movement for digitizer is recorded using an electronically active grid within the digitizing tablet. A mouse like device, called a puck, is connected to the tablet, and is moved along the tablet to different locations on a map that is attached to the tablet. Digitizing pucks contain a crosshair device, encased in glass or clear plastic that allows the operator to place the puck exactly over individual map elements.

This Image Shows How to Operate Puck over Map

The puck has buttons that indicate the beginnings and endings of lines or polygons, or explicitly define left and right polygons, and so on. How the digitizer buttons are used is largely determined by the GIS software requirements. Digitizing tablets come with rigid or flexible tablets and can range from small page-sized formats to very large formats. The smaller the digitizer the lower the cost.

Scanners

Scanners are more advanced input device that perform much of the work with little help from the user. Scanners come in three general types:

Types of Scanners

Line Following Scanners

As the name implies, line following scanners are placed on small wheels, tracking by laser or other guiding mechanism. At different intervals, these devices send a signal to the computer that records the digitizer coordinates at each of the sample location. Line following scanners requires more technician intervention because they must be manually placed on each new line to keep the scanning process going. Line following scanners produce vector output.

This Image Shows Line Following Scanner Produce Vector Outpu …

Flatbed Scanners

These scanners range from small units to large commercial scanners. A flatbed scanner is made up of a glass pane and a moving optical CCD (Charged Coupled Device) array. CCD technology is not like commonly available in digital cameras and remote sensing devices. The commercial flatbed scanner scans the map or image. Depending on the amount of memory and the quality of the original image or map, these devices can produce very good resolutions. The increased resolution results in very large images that can range up to many gigabytes.

This Image Shows Flatbed Scanners

Drum Scanners

A type of scanner in which a hard-copy image or map is attached to a cylinder that spins while a sensor captures a digital image from the surface of the page. Drum scanners spin your film around on a drum while a fixed laser or other beam of light looks at the art as it spins. The beam is them picked up by a very sensitive vacuum tube called a Photo Multiplier Tube (PMT) . This big single, fixed tube is much more sensitive to light than any of the teeny-tiny pixels on a CCD and therefore can see a broader range of light from white to black, and sees it without the noise of a CCD. In this flatbed scanner and drum scanner produce raster output.

This Image Shows Drum Scanner It Produce Raster Output

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